Synthesis of yttrium clusters

We report on the synthesis of Y nanoclusters and a particular chemical soli d-state reaction of these clusters YH2 double left right arrow YH3, which h as recently received increasing interest in the case of continuous thin fil ms, We used a novel type of laser ablation cluster source to synthesize Y-c lusters of about 25-30 nm average size at different Ar background gas press ures to hydrogenize them in situ. The clusters were characterized by electr on microscopy and optical spectroscopy. It was found that clusters prepared in higher Ar gas pressure consist of Y-core and Y2O3-shell contrary to Y-c lusters synthesized at low Ar gas conditions. Analysis of corresponding ext inction spectra were made by Mie theory calculations. Reaction with hydroge n was observed only for deposited Y-clusters which were hydrogenated at roo m temperature by adding atomic H. In a first step the metallic dihydride (Y H2) is formed. In a second step, additional H can form YH3-x (x < 1 to x mu ch less than 1). The latter compound is electrically isolating. The fascina ting properties of the last reaction are its reversibility at room temperat ure and the combination of a structural phase transition and a metal/non-me tal transition. The reversible phase transition was monitored by the optica l spectra which exhibit several strong and selective Mie resonances. (C) 20 01 Elsevier Science Ltd. All rights reserved.